CVE-2025-59438
📋 TL;DR
Mbed TLS versions through 3.6.4 contain a timing side-channel vulnerability in RSA decryption with PKCS#1 v1.5 padding. This allows attackers to potentially extract private keys by measuring decryption timing differences. Any system using vulnerable Mbed TLS for RSA operations is affected.
💻 Affected Systems
- Mbed TLS
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of RSA private keys, enabling decryption of captured traffic, impersonation of servers, or signing malicious code.
Likely Case
Partial key recovery requiring significant computational resources and network access, potentially leading to targeted decryption of specific messages.
If Mitigated
Minimal impact with proper network segmentation, key rotation, and monitoring for unusual decryption patterns.
🎯 Exploit Status
Exploitation requires precise timing measurements and multiple decryption attempts. Practical attacks are challenging but theoretically possible.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.6.5 and later
Vendor Advisory: https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2025-10-invalid-padding-error/
Restart Required: No
Instructions:
1. Update Mbed TLS to version 3.6.5 or later. 2. Recompile any applications using Mbed TLS. 3. Deploy updated binaries. 4. Consider rotating RSA keys as precaution.
🔧 Temporary Workarounds
Disable RSA PKCS#1 v1.5 Padding
allConfigure applications to use RSA-PSS or OAEP padding instead of PKCS#1 v1.5
Modify application configuration to use MBEDTLS_RSA_PKCS_V21 instead of MBEDTLS_RSA_PKCS_V15
🧯 If You Can't Patch
- Implement network segmentation to limit access to vulnerable services
- Monitor for unusual RSA decryption patterns and failed decryption attempts
🔍 How to Verify
Check if Vulnerable:
Check Mbed TLS version with: mbedtls_version_check() or examine build configuration for RSA PKCS#1 v1.5 usageCheck Version:
grep MBEDTLS_VERSION_STRING mbedtls/include/mbedtls/version.hVerify Fix Applied:
Verify version is 3.6.5 or later and confirm RSA operations use constant-time implementations📡 Detection & Monitoring
Log Indicators:
- Multiple failed RSA decryption attempts
- Unusual timing patterns in decryption operations
Network Indicators:
- Repeated connection attempts to RSA-enabled services with malformed padding
SIEM Query:
source="*mbedtls*" AND (event="decryption_failed" OR event="padding_error") | stats count by src_ip